Masterbatch and polymer composition

ABSTRACT

The present invention relates to a method of preparing a biodegradable polymer composition, said method comprising melt mixing a first biodegradable polyester and a masterbatch, wherein said masterbatch has been formed separately by melt mixing in the presence of a transesterification catalyst a polysaccharide, a second biodegradable polyester and a biodegradable polymer having pendant carboxylic acid groups.

FIELD OF THE INVENTION

The present invention relates generally to biodegradable polymercompositions. In particular, the invention relates to a method ofpreparing a biodegradable polymer composition, to the use of amasterbatch in the manufacture of the polymer composition, to a methodof preparing the masterbatch, and to the masterbatch.

BACKGROUND OF THE INVENTION

The disposal of consumer waste has become a significant problem in manyindustrialised countries. For example, there are relatively few sitesthat remain available for landfill in places such as Europe and Japan. Aconsiderable volume of consumer waste is made up of polymeric material,and there has been a concerted effort to introduce polymer recyclingstrategies to reduce such polymer waste going to landfill. However,unlike other materials such as glass, wood and metal, the recycling ofpolymers can be problematic. For example, polymer recycling techniquestypically require the polymers to be sorted according to their chemicalcomposition. However, due to the diverse array of different commercialpolymers it can be difficult to separate polymer materials from thewaste stream in this manner. Furthermore, most polymer recyclingtechniques involve a melt processing stage which can reduce the physicaland mechanical properties of the polymer. Recycled polymers thereforetend to have inferior properties and this can limit the range ofapplications in which they can be employed.

Apart from problems associated with recycling waste polymer materials,the majority of polymers currently being used are derived frompetroleum-based products, making their long-term manufactureunsustainable.

In response to these issues, there has been a marked increase inresearch directed toward developing biodegradable polymers that can atleast in part be manufactured using renewable resources. Unlikeconventional polymers, biodegradable polymers can be more readilydegraded through the action of microorganisms to produce low molecularweight products that present little, if any, environmental concern,Furthermore, through the action of biodegradation the volume occupied bysuch polymers in waste streams is significantly reduced.

Much of the research to-date in the field of biodegradable polymers hasfocussed on utilising naturally occurring bio-polymers such aspolysaccharides. Perhaps the most widely studied polysaccharide in thisregard is starch. Starch is a particularly suitable bio-polymer in thatit is derived from renewable resources (i.e. plant products), readilyavailable and relatively inexpensive. However, the physical andmechanical properties of starch in its native form are relatively poorcompared with those of conventional petroleum based (i.e. “synthetic”)polymers.

A number of techniques have been developed to improve the physical andmechanical properties of native starch. One approach has involvedconverting native starch into a thermoplastically processible starch(TPS). For example, PCT/WO90/05161 discloses a process for producing TPSwhich comprises melt mixing starch having a low water content with aplasticiser such as glycerol. Although the physical and mechanicalproperties of such TPS polymers are substantially better than nativestarch, these polymers typically have poor water resistance and cantherefore only be used in limited applications.

The water resistance of TPS polymers can be improved by blending thesepolymers with other thermoplastic polymers such as polyolefins. However,the biodegradability of these TPS polymer blends can he adverselyaffected due to the fact that polymers that are usually blended with theTPS are relatively non-biodegradable. Furthermore, the physical andmechanical properties of such TPS polymer blends are often quite poordue to the immiscibility of polymers employed in making the blends. Inparticular, polysaccharides such as starch and TPS are relativelyhydrophilic, whereas most synthetic thermoplastic polymers arerelatively hydrophobic. Accordingly, melt blending of starch or TPS withother thermoplastic polymers typically results in the formation of amulti-phase morphology having a high interfacial tension which cannegatively impact on the physical and mechanical properties of theresulting polymer blend.

Attempts have been made to improve the biodegradability and the physicaland mechanical properties of TPS polymer blends. For example, U.S. Pat.No. 5,844,023 discloses a biologically degradable polymer mixturecomprising a biodegradable polyester, a TPS and a “polymer phasemediator”. The polymer mixture is said to be readily biodegradable andthe polymer phase mediator is said to promote coupling of hydrophobicpolyester phase and hydrophilic TPS phase thereby improving the physicaland mechanical properties of the polymer mixture. A biodegradablepolymer composition disclosed in the US reference is formed through meltmixing a thermoplastic polyester with TPS. In this case, the polymerphase mediator is said to be formed in situ during this melt mixingprocess through transesterification between some of the polyester andsome of the TPS. Formation of the phase mediator in this way isconsidered difficult to control, and the process is believed to providea limited reduction in the interfacial tension between the immisciblepolymer phases.

Despite representing an advance in the field of biodegradable polymers,due to only a marginal improvement in phase coupling, the physical andmechanical properties of such polyester/TPS blends are still relativelypoor compared with conventional petroleum based polymers. To compensatefor this, such polyester/TPS blends are typically prepared with quitelow levels of starch. However, lowering the starch content of thecomposition increases its cost and can reduce its biodegradability.

Accordingly, there remains a need to develop alternative biodegradablepolymer compositions having good physical and mechanical properties.

SUMMARY OF THE INVENTION

The present invention provides a method of preparing a biodegradablepolymer composition, said method comprising melt mixing a firstbiodegradable polyester and a masterbatch, wherein said masterbatch hasbeen formed separately by melt mixing in the presence of atransesterification catalyst a polysaccharide, a second biodegradablepolyester and a biodegradable polymer having pendant carboxylic acidgroups.

In one embodiment of the invention, the masterbatch provides the onlysource of polysaccharide that is melt mixed with the first biodegradablepolyester to form the biodegradable polymer composition.

It has now been found that a polymer composition having excellentbiodegradability and physical and mechanical properties can be preparedusing a masterbatch that has been formed separately through melt mixinga polysaccharide, a biodegradable polyester and a biodegradable polymerhaving pendant carboxylic acid groups in the presence of atransesterification catalyst.

Accordingly, the invention also provides a masterbatch suitable for usein preparing a biodegradable polymer composition, said masterbatchcomprising the following components and/or their transesterificationreaction product: (a) polysaccharide; (b) biodegradable polyester; (c)biodegradable polymer having pendant carboxylic acid groups; and (d)transesterification catalyst.

Preferably, the total mass of components (a)-(d) and/or theirtransesterification reaction product in the masterbatch represents atleast 50 wt. % of the total mass of the masterbatch.

The invention further provides a method of preparing a masterbatchsuitable for use in the manufacture of a biodegradable polymercomposition, said method comprising melt mixing in the presence of atransesterification catalyst a polysaccharide, a biodegradable polyesterand a biodegradable polymer having pendant carboxylic acid groups.

The invention also provides the use of the masterbatch in themanufacture of a biodegradable polymer composition, said masterbatchbeing melt mixed with a biodegradable polyester.

In an embodiment of the invention, use of the masterbatch in themanufacture of a biodegradable polymer composition is such that themasterbatch provides the only source of polysaccharide that is meltmixed with the polyester to form the biodegradable polymer composition.

It has been found that a masterbatch in accordance with the inventioncan be readily melt mixed with a biodegradable polyester to afford abiodegradable polymer composition that exhibits improved compatibilitybetween its constituent components, relative to biodegradable polymercompositions comprising a polysaccharide and a polyester that areprepared by conventional means. The improved compatibility betweencomponents in polymer compositions of the invention is at least in partbelieved to be responsible for the compositions excellent physical andmechanical properties. The improved compatibility also enables thecompositions to be formulated with a relatively high polysaccharidecontent and this can advantageously reduce the cost of the compositionand improve its biodegradability.

Without wishing to be limited by theory, it is believed that thebiodegradable polymer having pendant carboxylic acid groups facilitatestransesterification between the polysaccharide and the biodegradablepolyester during preparation of the masterbatch. In particular, it isbelieved that the pendant carboxylic acid groups positioned along thepolymeric backbone of the biodegradable polymer interact throughhydrogen bonding and/or condensation/transesterification reactions withthe polysaccharide to promote the formation and/or retention of a highlynon-crystalline or destructured form of the polysaccharide. In thisform, the polysaccharide can more readily undergo transesterificationwith the biodegradable polyester to thereby minimise the presence of inthe masterbatch of uncompatibilised polysaccharide. This in turn isbelieved to give rise to the improved compatibility between theconstituent components of the masterbatch and biodegradable polymercomposition of the invention.

Further aspects of the invention are described below.

DETAILED DESCRIPTION OF THE INVENTION

Those skilled in the art will appreciate that the term “biodegradable”does not have a universal definition. For avoidance of any doubt, theterm “biodegradable” used herein association with the term “polymer”,“polymer composition” or specific polymer materials such as a“polysaccharide” and “polyester”, is intended to denote a material thatmeets the biodegradability criteria specified in EN 13432 or ASTM 6400.In other words, a polymer is considered to be biodegradable if, uponexposure to a composting environment, 90% of it disintegrates intoparticles having an average size of less than 2 mm within twelve weeks,and after six months at least 60% of it, in the case of ASTM 6400, or atleast 90% of it, in the case of EN 13432, has degraded into carbondioxide and/or water. Preferably, biodegradable polymer compositions inaccordance with the invention will meet the more stringentbiodegradability criteria set forth in EN 13432.

As used herein, reference to a biodegradable polymer having “pendantcarboxylic acid groups” is intended to mean that the carboxylic acidgroups (i.e. —COOH) are present as substituents along the polymericbackbone of a biodegradable polymer. The acid groups may be attacheddirectly to the polymeric back bone or attached to the backbone by aspacer group such as for example an alkyl group.

The method of preparing the biodegradable polymer composition inaccordance with the invention comprises melt mixing a firstbiodegradable polyester and a masterbatch as described. Melt mixing maybe performed using techniques and equipment well known in the art.Preferably, melt mixing is achieved using continuous extrusionequipment, such as twin screw extruders, single screw extruders, othermultiple screw extruders or Farell continuous mixers. Melt mixing isconducted for sufficient time and at a suitable temperature to promoteintimate blending between the first biodegradable polyester and themasterbatch, Those skilled in the art will appreciate that melt mixingis generally performed within a suitable temperature range and that thisrange will vary depending upon the nature of the polymer(s) beingprocessed.

An advantage of preparing a biodegradable polymer composition inaccordance with the invention is that melt mixing may be performed at aminimum melt processing temperature. This is in contrast with methodswhere a polysaccharide (or TPS) per se is directly melt mixed with apolyester to prepare a biodegradable polymer composition (e.g. as inU.S. Pat. No. 5,844,023). Using this latter type of methodology, it willtypically be necessary to employ temperatures above the minimum meltprocessing temperature to promote transesterification between thepolysaccharide (or TPS) and polyester and form compatibiliser in situ. Anotable disadvantage of performing the melt mixing process at atemperature above the minimum processing temperature is that the bulkpolyester and polysaccharide (or TPS) can thermally degrade. This canhave the effect of reducing the physical and mechanical properties ofthe resulting polymer composition.

Given that there is no need to form compatibiliser in situ during meltmixing of the first polyester and masterbatch in accordance with theinvention, high melt mixing temperatures can advantageously be avoided.

As used herein, the expression “minimum melt processing temperature” ofa polymer or polymer composition is considered to be the lowesttemperature or temperature range at which that polymer or compositioncan be maintained to enable it to be effectively melt processed whileminimising or avoiding thermal degradation of the polymer orcomposition. The minimum melt processing temperature will of course varydepending upon the materials being processed, and this can be readilydetermined by a person skilled in the art.

In some cases it may be desirable to vent or apply vacuum to the meltmixing process to allow volatile components such as water to be removedfrom the polymer melt.

The first biodegradable polyester used in accordance with the inventionmay be any biodegradable polyester that can be subjected to melt mixing.Examples of suitable biodegradable polyesters include, but are notlimited to, polycaprolactone (PCL) as sold by Union Carbide under thetrade name Tone™ (e.g. Tone P-300, P-700, P-767 and P-787 having aweight average molecular weight of about 10,000, 40,000, 43,000 and80,000, respectively), or those sold by Solvay under the trade name CAPA6800 and CAPA FB 100 having a molecular weight of 80,000 and 100,000Daltons, respectively; polylactic acid (PLA) as sold under the tradename Natureworks™ PLA by Cargill; polyhydroxy butyrate (PHB) as soldunder the trade name Biocycle™ or Biomer by Biomer, Germany;polyethylene succinate (PES) and polybutylene succinate (PBS) as soldunder the trade name Bionolle™ by Showa Hi Polymer Company (e.g.Bionolle™ 1001 (PBS) and Bionelle™ 6000 (PES)); polybutylene adipate(PBA) as sold under the trade name Skygreen™ SG 100 from SK ChemicalsKorea; poly(butylene adipate/terephthalate) (PBAT) aliphatic/aromaticcopolyesters such as Ecoflex™ by BASF, or EnPOL™ G8060 and EnPOL™ 8000by Ire Chemical Ltd of Seoul; poly(hydroxybutyrate valerate) (PHBV) byMetabolix Inc. USA; cellulose acetate butyrate (CAB) and celluloseacetate propionate (CAP) supplied by Eastman Chemicals; or combinationsthereof.

When preparing the biodegradable polymer composition in accordance withthe invention, the first biodegradable polyester will generally be usedin an amount ranging from about 5 wt. % to about 90 wt. %, preferably inan amount ranging from about 20 wt. % to about 80 wt. %, more preferablyin an amount ranging from about 40 wt. % to about 70 wt. %, and themasterbatch will generally be used in an amount ranging from about 10wt. % to about 95 wt. %, preferably in an amount ranging from about 20wt. % to about 80 wt. %, more preferably in an amount ranging from about30 wt. % to about 60 wt. %, relative to the total mass of the firstbiodegradable polyester and the masterbatch, and such that the totalmass of these two components represents at least 65 wt. %, preferably atleast 70 wt. %, more preferably at least 75 wt. %, most preferably atleast 80 wt. %, of the total mass of the biodegradable polymercomposition. Where the total mass of the biodegradable polymercomposition is not made up entirely of the first biodegradable polyesterand the masterbatch, the remaining components of the composition willinclude one or more additives described in more detail below.

In one embodiment of the invention, the first biodegradable polyesterand the masterbatch make up 100 wt. % of the biodegradable polymercomposition.

When preparing the biodegradable polymer composition, the firstbiodegradable polyester is melt mixed with the masterbatch. As usedherein, the term “masterbatch” is intended to mean a compositioncomprising a carrier polymer and one or more agents, where theconcentration of the one or more agents is higher than desired in afinal product, and which composition is subsequently let down in a basepolymer to produce the final product having the desired amount of theone or more agents. With particular reference to the present invention,the masterbatch may comprise a biodegradable polyester and abiodegradable polymer having pendant carboxylic acid groups as carrierpolymers and a polysaccharide as an agent.

As will be discussed in more detail below, by virtue of the manner inwhich it is prepared the masterbatch is believed to also comprise areaction product derived from at least some of the polysaccharideundergoing transesterification with the biodegradable polyester. Withoutwishing to be limited by theory, it may also be that in preparing themasterbatch all of the polysaccharide undergoes a degree oftransesterification with the biodegradable polyester. The biodegradablepolymer having pendant carboxylic acid groups may also take part in suchreactions. This of course needs to be taken into account when construingthe term “masterbatch” as it is defined directly above. Thus, thetransesterification reaction product between the polysaccharide and thebiodegradable polyester (and also possibly the biodegradable polymerhaving pendant carboxylic acid groups) is to be understood as taking thedual role of both carrier polymer and agent. In other words, as usedherein the term “masterbatch” is to be construed such that it embracesthe situation where aforementioned carrier polymer and agent is in facta reaction product between the polysaccharide, the biodegradablepolyester and possibly the biodegradable polymer having pendantcarboxylic acid groups.

Accordingly, the masterbatch may be described as comprising apolysaccharide, a biodegradable polyester, a biodegradable polymerhaving pendant carboxylic acid groups, a transesterification catalystand/or a reaction product derived from melt mixing these components inthe presence of the transesterification catalyst.

In the method of preparing the biodegradable polymer composition, themasterbatch is formed separately. By being “formed separately” is meantthat the masterbatch is prepared in advance and is subsequently meltmixed with the first biodegradable polyester. The masterbatch cantherefore be prepared and conveniently stored for future use.Alternatively, the masterbatch may be prepared and then immediatelycombined with the first biodegradable polyester in a melt mixingprocess.

The masterbatch used in accordance with the invention is prepared bymelt mixing, in the presence of a transesterification catalyst, a secondbiodegradable polyester, a polysaccharide and a biodegradable polymerhaving pendant carboxylic acid groups. Melt mixing may be performedusing equipment and techniques hereinbefore described,

The second biodegradable polyester used in preparing the masterbatch maybe selected as described above in respect of the first biodegradablepolyester. The second biodegradable polyester may be the same as ordifferent from the first biodegradable polyester. Unless otherwisestated, for convenience the first and second biodegradable polyesterswill hereinafter simply be referred to as the “biodegradable polyester”.

Suitable types of biodegradable polymer having pendant carboxylic acidgroups that may be used in preparing the masterbatch include, but arenot limited to, ethylene acrylic acid (EAA) copolymer, poly(EAA-vinylalcohol) (EAAVA), poly(acrylic acid) (PAA), poly(methacrylic acid)(PMA), ethylene-methacrylic acid copolymers (EMAA), andpoly(acrylamide-acrylic acid) (PAAA).

In preparing the masterbatch, the biodegradable polymer having pendantcarboxylic acid groups will generally used in an amount ranging fromabout 5 wt. % to about 35 wt. %, preferably from about 10 wt. % to about25 wt. %, more preferably from about 15 wt. % to about 25 wt. %,relative to the total mass of component used in preparing themasterbatch.

The biodegradable polymer having pendant carboxylic acid groups willgenerally have a melt flow index (MFI, as measured at 190° C. using 2.16Kg weight) of greater than about 15, preferably ranging from about 15 toabout 50, more preferably from about 15 to about 20.

The biodegradable polymer having pendant carboxylic acid groups willgenerally have a % acid value (as determined by ASTM D4094-00) ofgreater than about 7%, preferably greater than or equal to about 9%.

The polysaccharide used in preparing the masterbatch may be anypolysaccharide that can be subjected to melt mixing. The polysaccharidepreferably has a water content below about 1 wt. %, more preferablybelow about 0.5 wt. %. Suitable polysaccharides include, but are notlimited to, starch, glycogen, chitosan and cellulose.

A preferred polysaccharide for use in preparing the masterbatch isstarch. Starch is a particularly convenient polysaccharide in that it isrelatively inexpensive, it is derived from a renewable resource and itis readily available. Starch is found chiefly in seeds, fruits, tubers,roots and stem pith of plants, and is basically a polymer made up ofrepeating glucose groups linked by glueosidic linkages in the 1-4 carbonpositions. Starch consists of two types of alpha-D-glucose polymers:amylose, a substantially linear polymer with molecular weight of about1×10⁵; and amylopectin, a highly branched polymer with very highmolecular weight of the order 1×10⁷. Each repeating glucose unittypically has three free hydroxyl groups, thereby providing the polymerwith hydrophilic properties and reactive functional groups. Moststarches contain 20 to 30% amylose and 70 to 80% amylopectin. However,depending on the origin of the starch the ratio of amylose toamylopectin can vary significantly. For example, some corn hybridsprovide starch with 100% amylopectin (waxy corn starch), orprogressively higher amylose content ranging from 50 to 95%. Starchusually has a water content of about 15 wt. %. However, the starch canbe dried to reduce its water content to below 1%.

Starch typically exists in small granules having a crystallinity rangingfrom about 15 to 45%. The size of the granules may vary depending uponthe origin of the starch. For example, corn starch typically has aparticle size diameter ranging from about 5 to 40 μm, whereas potatostarch typically has a particle size diameter ranging from about 50 to100 μm. In this “native” form, starch can be difficult to melt process.To improve the melt processability of starch, the starch may beconverted to a TPS by means well known in the art. Thus, TPS may be usedas the polysaccharide in accordance with the invention. For example,native starch may be melt processed with one or more plasticisers suchas water, glycerine, di—or ethyleneglycol, trimethylene glycol, sorbitolor other low molecular weight polyether compounds.

Water is an excellent plasticiser for the manufacture of TPS. However,due to its relatively low boiling point, the presence of water aboveabout 1 wt. % in TPS can cause an undesirable degree of volatilisationof water during melt mixing. Furthermore, the presence of too much waterduring the preparation of the masterbatch or biodegradable polymercomposition can cause an undesirable degree of hydrolysis of thepolyester.

Preferred plasticisers for the manufacture of TPS include glyceroland/or sorbitol. These, and other suitable plasticisers are typicallyused in an amount ranging from about 5 wt. % to about 50 wt. %,preferably in an amount ranging from about 10 wt. % to about 40 wt. %,more preferably in an amount ranging from about 10 wt. % to about 30 wt.%, relative to the total mass of native starch.

Chemically modified starch may also be used as the polysaccharide inaccordance with the invention. Chemically modified starch includes, butis not limited to, oxidised starch, etherificated starch, esterifiedstarch, cross-linked starch or a combination of such chemicalmodifications (e.g., etherificated and esterified starch). Typically,modified starch is prepared by reacting the hydroxyl groups of thepolymer with one or more reagents. The degree of reaction, oftenreferred to the degree of substitution (DS), can significantly alter thephysicochemical properties of the modified starch compared with thecorresponding native starch. The DS for a native starch is designated as0, and can range up to 3 for a fully substituted modified starch. Wherethe substituent groups have hydrophobic character, a DS approaching 3can afford a modified starch that is relatively hydrophobic incharacter, Such modified starches can be more readily melt blended withthe second biodegradable polyester, relative to native starch.

A chemically modified starch may also be converted to TPS by melt mixingit with plasticiser as hereinbefore described. In this case, theaforementioned amounts of plasticiser used will be relative to the totalmass of the modified starch.

Starches that are chemically modified are preferably etherificated oresterified. Suitable etherificated starches include, but are not limitedto, those which are substituted with ethyl and/or propyl groups.Suitable esterified starches include, but are not limited to, those thatare substituted with acetyl, propanoyl and/or butanoyl groups.

Etherificated starches may be prepared using techniques well known inthe art, such as reacting starch with an appropriate alkylene oxide.Esterified starches may also be prepared using techniques well known inthe art, such as reacting starch with appropriate anhydride, carboxylicacid or acid chloride reagents.

When starch is used as the polysaccharide, it may be in its native form,in the form of a TPS, a chemically modified starch, or a combinationsuch starches may be used. In all cases, it is preferable that the watercontent of the starch is less than about 1 wt. %, preferably less thanabout 0.5 wt. %.

It will of course also be possible to form TPS during the melt mixingprocess used to prepare the masterbatch. For example, the method ofproducing the masterbatch may comprise melt mixing native starch and/orchemically modified starch, plasticiser, biodegradable polyester, abiodegradable polymer having pendant carboxylic acid groups and atransesterification catalyst.

Where a TPS is used in preparing the masterbatch and/or a plasticiserper se is used in preparing the masterbatch, the presence of plasticiserduring the melt mixing process is believed to further enhance theformation and/or retention of a highly non-crystalline or destructuredform of the polysaccharide.

Preferred types of starch materials include, but are not limited to,corn starch, potato starch, wheat starch, soybean starch, tapiocastarch, high-amylose starch or combinations thereof.

Preferably, the starch is corn starch, and more preferably the cornstarch is corn starch acetate such as that supplied by the ShanghaiDenaturalization Starch Company, Shanghai, (DS>0.08%, moisturecontent<14%),

The transesterification catalyst used in preparing the masterbatchfunctions to lower the melt processing temperature at which thematserbatch components may be melt mixed and undergo reaction comparedwith that which would be required to promote the same degree of reactionin the absence of the catalyst. While the catalyst is referred to as a“transesterification” catalyst, those skilled in the art will appreciatefrom the nature of components being melt mixed to prepare themasterbatch that other reactions such as condensation and ester exchangereactions may also take place. Thus, for convenience it is to beunderstood that reference herein to the term “transesterification” isintended to embrace other mechanisms of reaction that can occur betweenester, alcohol and acid groups such as ester exchange and condensationreactions.

Suitable transesterification catalysts include, but are not limited to,alkali metal hydroxides such as sodium and/or potassium hydroxide, Thetype of catalysts employed preferably has low ecotoxicity. Antimonybased transesterification catalysts will therefore not generally beused. The catalyst may be provided in solution, for example in anaqueous solution.

Those skilled in the art will appreciate that transesterificationbetween the polysaccharide and the biodegradable polyester or thebiodegradable polymer having pendant carboxylic acid groups willtypically result in the formation of a block co-polymer. The blockco-polymer(s) may function as a compatibiliser for any polysaccharide,biodegradable polyester and biodegradable polymer having pendantcarboxylic acid groups that have not undergone transesterification.Thus, irrespective of whether only part or all of the polysaccharideundergoes transesterification with the biodegradable polyester and/orthe biodegradable polymer having pendant carboxylic acid groups, themasterbatch is believed to present as a homogenous composition at leastin terms of these three components.

As a compatibiliser, the block co-polymer(s) formed during preparationof the masterbatch can be seen to comprise a section(s) or region(s)that is miscible with the polysaccharide and a section(s) or region(s)that is miscible with the biodegradable polyester and/or thebiodegradable polymer having pendant carboxylic acid groups. The blockco-polymer(s) can therefore function to decrease the interfacial tensionbetween and promote the coupling of immiscible polysaccharide andpolyester phases that may be present in the masterbatch or thebiodegradable polymer composition formed from the masterbatch.

As indicated above, when preparing the masterbatch the presence of thebiodegradable polymer having pendant carboxylic acid groups is believedto promote the formation of such block co-polymers, which in turn arebelieved to improve the compatibility between constituent components ofthe biodegradable polymer composition of the invention.

The masterbatch is therefore believed to comprise a highlycompatibilised mixture and/or transesterification reaction product ofpolysaccharide, biodegradable polyester and the biodegradable polymerhaving pendant carboxylic acid groups. However, the masterbatch per semay not exhibit sufficient physical and mechanical properties for use inmany applications. To provide a biodegradable polymer composition withimproved physical and mechanical properties, particularly in the areasof tensile strength and tensile elongation, the masterbatch can be meltmixed with the first biodegradable polyester. Excellent characteristicsof such polymer compositions are believed to be derived at least in partfrom properties imparted by the first biodegradable polyester and theability of the masterbatch to form a compatible blend with the firstbiodegradable polyester.

The ability of the masterbatch to form a relatively compatible blendwith the first biodegradable polyester is believed to represent animportant advantage of the present invention. In particular,conventional methods for preparing biodegradable polyester compositionstypically involve melt mixing a polysaccharide and a biodegradablepolyester, optionally with a compatibiliser, and promoting couplingbetween the hydrophobic polyester phase and the hydrophilicpolysaccharide phase during that melt mixing step. In contrast, whenpreparing the polymer composition in accordance with the invention themasterbatch can and preferably does provide the only source ofpolysaccharide that is melt mixed with the first biodegradablepolyester, and this polysaccharide is already well compatibilised and/orhas undergone transesterification with a biodegradable polyester and/ora biodegradable polymer having pendant carboxylic acid groups. Thus,components being melt mixed during formation of the biodegradablecomposition may already be relatively compatible. This simplifies andimproves the efficiency of preparing the composition and is believed toprovide a composition having excellent physical and mechanicalproperties.

However, in the case where the masterbatch does not provide the onlysource of polysaccharide that is melt mixed with the first biodegradablepolyester in preparing the biodegradable polymer composition inaccordance with the invention, the well compatibilised masterbatch canadvantageously in itself function as a compatabiliser for the furthersource of polysaccharide and the first biodegradable polyester.

Compatibilisation between the components present in the masterbatch andthe biodegradable polymer composition can be readily determinedexperimentally by imaging the composition and/or by measuring thephysical and mechanical properties of the composition. For example, themasterbatch or composition may be cryogenically frozen, fractured thenview under a scanning electron microscope to evaluate the level ofadhesion between the dispersed phase and the continuous phase.

Where the polysaccharide used to prepare the masterbatch is nativestarch, as indicated above transesterification between the starch, thebiodegradable polyester and possibly the biodegradable polymer havingpendant carboxylic acid groups can be further enhanced by introducingduring melt mixing a plasticiser such as glycerol and/or sorbitol. Inthis case, the plasticiser will generally be used in amountshereinbefore described. Preferably, this will result in an amount ofplasticiser ranging from 10 wt. % to about 20 wt. %, relative to thetotal mass of the masterbatch.

Where a mixture of glycerol and sorbitol plasticisers are used, it ispreferable that they be used in a weight ratio ranging from about 2:1 toabout 3:1.

Transesterification between the starch, the biodegradable polyester andpossibly the biodegradable polymer having pendant carboxylic acid groupscan also be further enhanced by using chemically modified starch. Inthis case, it is preferable to use esterified starch as hereinbeforedescribed having a DS ranging from about 0.1 to about 1, more preferablyranging from about 0.5 to about 1. It may also be preferable tointroduce with the modified starch during melt mixing a plasticiser ashereinbefore described.

As part of the method of preparing the masterbatch, it may also bedesirable to use a relatively low weight average molecular weightbiodegradable polyester (e.g. ranging from about 30,000 to about 40,000)in order to further enhance transesterification of the polysaccharide.In this case, it is preferred that the first biodegradable polyester hasa weight average molecular weight ranging from about 80,000 to about1000,000.

When preparing the biodegradable polymer composition in accordance withthe invention, there is no particular limitation on the polysaccharidecontent of the masterbatch. However, the masterbatch will generally beprepared using a relatively high proportion of polysaccharide in orderto maximise the amount of polysaccharide that is ultimately introducedto the biodegradable polymer composition via the masterbatch.

When preparing the biodegradable polymer composition in accordance withthe invention, the masterbatch used will generally be preparedseparately by melt mixing about 20 wt. % to about 70 wt. %, preferablyabout 40 wt. % to about 65 wt. %, more preferably about 45 wt. % toabout 60 wt. % of the polysaccharide, about 20 wt. % to about 70 wt. %,preferably about 25 wt. % to about 50 wt. %, more preferably about 25wt. % to about 40 wt. % of the second biodegradable polyester, about 5wt. % to about 50 wt. %, preferably about 10 wt. % to about 40 wt. %,more preferably about 15 wt. % to about 30 wt. % of the biodegradablepolymer having pendant carboxylic acid groups, and about 0.1 wt. % toabout 1 wt. %, preferably about 0.1 wt. % to about 0.5 wt. %, morepreferably about 0.15 wt. % to about 0.5 wt. % of thetransesterification catalyst, relative to the total mass of thepolysaccharide, the second biodegradable polyester, the biodegradablepolymer having pendant carboxylic acid groups, and thetransesterification catalyst, and such that the total mass of these fourcomponents and/or their transesterification reaction product representsat least 50 wt. %, preferably at least 60 wt. %, more preferably atleast 65 wt. %, most preferably at least 70 wt. %, of the total mass ofthe masterbatch. Where the total mass of the masterbatch is not made upentirely of the polysaccharide, the second biodegradable polyester, thebiodegradable polymer having pendant carboxylic acid groups, and thetransesterification catalyst, the remaining components of themasterbatch will include one or more additives such as plasticiserhereinbefore described and other additives described in more detailbelow.

The invention also provides a masterbatch suitable for use in preparinga biodegradable polymer composition, said masterbatch comprising thefollowing components and/or their transesterification reaction product:(a) about 20 wt. % to about 70 wt. %, preferably about 40 wt. % to about65 wt. %, more preferably about 45 wt. % to about 60 wt. % ofpolysaccharide; (b) about 20 wt. % to about 70 wt. %, preferably about25 wt. % to about 50 wt. %, more preferably about 25 wt. % to about 40wt. % of biodegradable polyester; (c) about 5 wt. % to about 50 wt. %,preferably about 10 wt. % to about 40 wt. %, more preferably about 15wt. % to about 30 wt. % of the biodegradable polymer having pendantcarboxylic acid groups, and (d) 0.1 wt. % to 1 wt. %, preferably 0.1 wt.% to 0.5 wt. %, more preferably 0.15 wt. % to 0.5 wt. % oftransesterification catalyst; relative to the total mass of thepolysaccharide, the second biodegradable polyester, the biodegradablepolymer having pendant carboxylic acid groups, and thetransesterification catalyst, and such that the total mass of these fourcomponents and/or their transesterification reaction product representsat least 50 wt,%, preferably at least 60 wt. %, more preferably at least65 wt. %, most preferably at least 70 wt. %, of the total mass of themasterbatch. Where the total mass of the masterbatch is not made upentirely of the polysaccharide, the second biodegradable polyester, thebiodegradable polymer having pendant carboxylic acid groups, and thetransesterification catalyst, the remaining components of themasterbatch will include one or more additives such as plasticiserhereinbefore described and other additives described in more detailbelow.

The invention further provides a masterbatch suitable for use inpreparing a biodegradable polymer composition, said masterbatchcomprising the following components and/or their transesterificationreaction product: (a) 45 wt. % to 70 wt. %, preferably 50 wt. % to 65wt. %, more preferably 50 wt. % to 60 wt. % of polysaccharide; (b) 10wt. % to 50 wt. %, preferably 10 wt. % to 40 wt. %, more preferably 10wt. % to 30 wt. % of biodegradable polyester; (c) 5 wt. % to 50 wt. %,preferably 10 wt. % to 40 wt. %, more preferably 15 wt. % to 30 wt. % ofthe biodegradable polymer having pendant carboxylic acid groups, and (d)0.1 wt. % to 1 wt. %, preferably 0.1 wt. % to 0.5 wt. %, more preferably0.15 wt. % to 0.5 wt. % of transesterification catalyst; relative to thetotal mass of the polysaccharide, the biodegradable polyester, thebiodegradable polymer having pendant carboxylic acid groups, and thetransesterification catalyst, and such that the total mass of these fourcomponents and/or their transesterification reaction product representsat least 60 wt. %, preferably at least 65 wt. %, more preferably atleast 70 wt. %, most preferably at least 75 wt. % of the total mass ofthe masterbatch. Where the total mass of the masterbatch is not made upentirely of the polysaccharide, the biodegradable polyester, thebiodegradable polymer having pendant carboxylic acid groups, and thetransesterification catalyst and/or their transesterification reactionproduct, the remaining components of the masterbatch will includeadditives such as plasticiser hereinbefore described and other additivesdescribed in more detail below.

The invention further provides a method of preparing a masterbatchsuitable for use in the manufacture of a biodegradable polymercomposition, said method comprising melt mixing about 20 wt. % to about70 wt. %, preferably about 40 wt. % to about 65 wt. %, more preferablyabout 45 wt. % to about 60 wt. % of the polysaccharide, about 20 wt. %to about 70 wt. %, preferably about 25 wt. % to about 50 wt. %, morepreferably about 25 wt. % to about 40 wt. % of the second biodegradablepolyester, about 5 wt. % to about 50 wt. %, preferably about 10 wt. % toabout 40 wt. %, more preferably about 15 wt. % to about 30 wt. % of thebiodegradable polymer having pendant carboxylic acid groups, and about0.1 wt. % to about 1 wt. %, preferably about 0.1 wt. % to about 0.5 wt.%, more preferably about 0.15 wt. % to about 0.5 wt. % of thetransesterification catalyst, relative to the total mass of thepolysaccharide, the second biodegradable polyester, the biodegradablepolymer having pendant carboxylic acid groups, and thetransesterification catalyst, and such that the total mass of these fourcomponents and/or their transesterification reaction product representsat least 50 wt. %, preferably at least 60 wt. %, more preferably atleast 65 wt. %, most preferably at least 70 wt. %, of the total mass ofthe masterbatch. Where the total mass of the masterbatch is not made upentirely of the polysaccharide, the second biodegradable polyester, thebiodegradable polymer having pendant carboxylic acid groups, and thetransesterification catalyst, the remaining components of themasterbatch will include one or more additives such as plasticiserhereinbefore described and other additives described in more detailbelow.

The invention also provides a method of preparing a masterbatch suitablefor use in the manufacture of a biodegradable polymer composition, saidmethod comprising melt mixing 45 wt. % to 70 wt. %, preferably 50 wt. %to 65 wt. %, more preferably 50 wt. % to 60 wt. % of polysaccharide, 10wt. % to 50 wt. %, preferably 10 wt. % to 40 wt. %, more preferably 10wt. % to 30 wt. % of a biodegradable polyester, about 5 wt. % to about50 wt. %, preferably about 10 wt. % to about 40 wt. %, more preferablyabout 15 wt. % to about 30 wt. % of the biodegradable polymer havingpendant carboxylic acid groups, and 0.1 wt. % to 1 wt. %, preferably 0.1wt. % to 0.5 wt. %, more preferably 0.15 wt. % to 0.5 wt,% oftransesterification catalyst, relative to the total mass of thepolysaccharide, the biodegradable polyester and the transesterificationcatalyst, and such that the total mass of these four components and/ortheir transesterification reaction product represents at least 60 wt. %,preferably at least 65 wt. %, more preferably at least 70 wt. %, mostpreferably at least 75 wt. % of the total mass of the masterbatch. Wherethe total mass of the masterbatch is not made up entirely of thepolysaccharide, the biodegradable polyester, the biodegradable polymerhaving pendant carboxylic acid groups, and the transesterificationcatalyst, the remaining components of the masterbatch will include oneor more additives such as plasticiser hereinbefore described and otheradditives described in more detail below.

The masterbatch may be provided in any suitable form that can besubsequently melt mixed with a biodegradable polyester to form thebiodegradable polymer composition in accordance with the invention.Generally, the masterbatch will be provided in the form of pellets.

The biodegradable polymer composition, masterbatch and methods for thepreparation thereof in accordance with the invention may comprise a stepof introducing, respectively, one or more additives provided that suchadditives do not adversely impact on the biodegradability of the polymercomposition. Preferably, the additives are only included in themasterbatch. Such additives may include fillers such as calciumcarbonate, silicone dioxide, talc, clays such as montmorillonite,titanium dioxide and natural fibres such as wood powder, paper pulpand/or other cellulosic materials; pigments; anti-static agents;stabilisers; blowing agents; processing aids such as lubricants;fluidity enhancers; anti-retrogradation additives; plasticisers ashereinbefore described; and antiblocking agents such as silicon dioxide.

Common lubricants include, but are not limited to, calcium stearate,steric acid, magnesium stearate, sodium stearate, oxidised polyethylene,oleamide, stearamide and erucamide. A lubricant will generally be usedin an amount to provide for an amount ranging from about 0.2 wt. % to0.7 wt. % in the biodegradable polymer composition.

Common fluidity enhancers include, but are not limited to,monoglycerides, glucose fat diethylene glycol dinitrate and productssold under the trade name Siben-60 or Siben-80. A fluidity enhancer willgenerally be used in an amount to provide for an amount ranging fromabout 1 wt. % to about 2 wt. % in the biodegradable polymer composition.

A common anti-retrogradation additive includes, but is not limited to, adistilled monoglyceride. Anti-retrogradation additives will generally beused in an amount to provide for an amount ranging from about 0.5 wt. %to about 1 wt. % in the biodegradable polymer composition. An additivesuch as distilled monoglyceride is also believed to assist with thedispersability and stabilisation of the polysaccharide.

An antiblocking agent such as silicon dioxide may be used in an amountto provide for an amount ranging from about 0.25 wt. % to 0.5 wt. % inthe biodegradable polymer composition.

The method of preparing the biodegradable polymer composition inaccordance with the invention may also comprise melt mixing with themasterbatch and the biodegradable polyester a second or furtherpolysaccharide. A suitable second or further polysaccharide may beselected from the polysaccharides hereinbefore described. In this case,the polysaccharide will generally be used in an amount up to about 40wt. %, preferably up to about 30 wt. %, more preferably no more thanabout 20 wt. %, relative to the total mass of the biodegradablepolyester composition.

To minimise an undesirable degree of hydrolysis occurring during meltmixing, the first biodegradable polyester, the polysaccharide, themasterbatch and any other additives used in preparing the polymercomposition will preferably each have a water content of less than about2 wt. %, more preferably of less than about 1 wt. %, most preferably ofless than about 0.6 wt. %.

In a preferred embodiment of the invention, the method of preparing thebiodegradable polymer composition comprises melt mixing about 5 wt. % toabout 90 wt. % of a first biodegradable polyester and about 10 wt. % toabout 95 wt. % of a masterbatch, relative to the total mass of the firstbiodegradable polyester and the masterbatch, and such that the totalmass of these two components represents at least 95 wt. % of the totalmass of the biodegradable polymer composition, wherein said masterbatchhas been formed separately by melt mixing about 20 wt. % to about 70 wt.% of a polysaccharide and about 10 wt. % to about 70 wt. % of a secondbiodegradable polyester, about 5 wt. % to about 25 wt. % of thebiodegradable polymer having pendant carboxylic acid groups, about 5 wt.% to about 50 wt. % of plasticiser in the presence of about 0.1 wt. % toabout 1 wt. % of a transesterification catalyst, relative to the totalmass of the polysaccharide, the second biodegradable polyester, thetransesterification catalyst, the plasticiser and the biodegradablepolymer having pendant carboxylic acid groups, and such that the totalmass of these five components represents at least 95 wt. % of the totalmass of the masterbatch.

The biodegradable polymer composition prepared in accordance with theinvention has excellent physical and mechanical properties and isreadily biodegradable. The composition can be conveniently processedusing conventional polymer converting techniques such as extrusion,injection moulding, and thermoforming. The composition is particularlysuited for manufacturing film and sheet that may be converted intopackaging materials. In this case, PCL, PBAT, PHBV, PES and PBS arepreferably used as the biodegradable polyester. The composition may alsobe used in the manufacture of food utensils such as cups, plates,cutlery and trays. In this case, the biodegradable polyester used inpreferably PLA and CAB.

The invention also provides a sheet or film formed from thebiodegradable polymer composition prepared in accordance with theinvention.

The biodegradable polymer composition may be provided in any suitableform that can be processed into a desired product such as sheet or film.Generally, the composition will be provided in the form of pellets.

Embodiments of the invention are further described with reference to thefollowing non-limiting examples.

EXAMPLE 1: PREPARATION OF MASTERBATCH FROM STARCH AND PBS (MB-1)

35 kg of acetic ester starch (DS of 0.5) having a water content of lessthan 1 wt. %, 14 kg of glycerol, 6 kg of sorbitol, 0.8 kg of distilledmonoglyceride, 20 kg of ethylene acrylic acid (EEA) (9% acid, melt flowindex=20), 15 kg PBS (by Mitsubishi, Japan), 0.3 kg calcium stearate,0.2 kg steric acid, and 0.12 kg sodium hydroxide dissolved in a minimumamount of water were melt mixed in a ZSK-65 Twin Screw Extruder(L/D=48). Prior to melt mixing these components, the solid materialswere dry blended first in a high speed mixer and the liquid materialsthen added to provide for a uniform distribution of all components. Thetemperature profile of the extruder was set at 75° C./140° C./175°C./175° C./160° C./130° C. The rotation speed of the screw was set at200 rpm. A vacuum of −0.06 to −0.08 bar was applied during extrusion.The polymer melt was extruded as a strand, air cooled and cut intopellets. The masterbatch was found to have a melt flow index of >4 g/10min at 190° C. with 2.16 kg, and a water content of<0.2 wt. %.

EXAMPLE 2: PREPARATION OF A BIODEGRADABLE POLYMER COMPOSITION

A composition consisting of 45 wt. % MB-1, 35 wt. % PCL and 20 wt. %PBAT was first dry blended and then melt mixed using a ZSK-65 Twin ScrewExtruder with a rotational speed of 220 rpm. The temperature profile ofthe extruder was set at 80° C./130° C./165° C./165° C./155° C./130° C. Avacuum of −0.04 to −0.05 bar was applied during extrusion. The resultingextrudate was water cooled and cut into pellets and was found to have amelt flow index of 10 g/10 min, at 190° C. with 2.16 kg.

The polymer composition prepared in accordance with Example 2 was blowninto film having a thickness of approximately 15 micron. The resultingfilm was tested according to ASTM D-882 and found to exhibit a tensilestrength at break of >15 MPa and an elongation at break of >600%. Thefilm was also found to fully comply with the biodegradabilityrequirements of EN 13432.

A range of films formed from comparative commercially availablepolysaccharide/polyester polymer compositions sold under the trade nameMater-Bi, BioCorp, Eco Works and Eco Film were found to have anelongation at break when tested in accordance with ASTM D-882 of<400%.

EXAMPLE 3: PREPARATION OF A BIODEGRADABLE POLYMER COMPOSITION

A composition consisting of 45 wt. % MB-1 and 55 wt. % PHBV was firstdry blended and then melt mixed using a ZSK-65 Twin Screw Extruder witha rotational speed of 220 rpm. The temperature profile of the extruderwas set at 80° C./130° C./165° C./165° C./155° C./130° C. A vacuum of−0.04 to −0.05 bar was applied during extrusion. The resulting extrudatewas water cooled and cut into pellets and was found to have a melt flowindex of 10 g/10 min, at 190° C. with 2.16 kg.

The polymer composition prepared in accordance with Example 3 was blowninto film having a thickness of approximately 15 micron. The resultingfilm was tested according to ASTM D-882 and found to exhibit a tensilestrength at break of >15 MPa and an elongation at break of >500%. Thefilm was also found to fully comply with the biodegradabilityrequirements of EN 13432.

EXAMPLE 4: PREPARATION OF A BIODEGRADABLE POLYMER COMPOSITION

A composition consisting of 30 wt. % MB-1 and 70 wt. % PLA was first dryblended and then melt mixed using a ZSK-65 Twin Screw Extruder with arotational speed of 220 rpm. The temperature profile of the extruder wasset at 90° C./160° C./185° C./185° C./175° C./165° C. A vacuum of −0.04to −0.05 bar was applied during extrusion. The resulting extrudate waswater cooled and cut into pellets and was found to have a melt flowindex of 8-10 g/10 min, at 190° C. with 2.16 kg.

The polymer composition prepared in accordance with Example 4 was formedinto a cast extruded sheet. The resulting sheet was tested according toASTM D-882 and found to exhibit a tensile strength at break of >20 MPa,an elongation at break of >350%, and a dart drop impact strength (inaccordance with GB1843) of >20 kJ/m². The sheet was also found to fullycomply with the biodegradability requirements of EN 13432.

EXAMPLE 5: PREPARATION OF A BIODEGRADABLE POLYMER COMPOSITION

A composition consisting of 28 wt. % MB-1, 8 wt. % PCL and 65 wt. % PLAwas first dry blended and then melt mixed using a ZSK-65 Twin ScrewExtruder with a rotational speed of 220 rpm. The temperature profile ofthe extruder was set at 90° C./160° C./185° C./185° C./175° C./165° C. Avacuum of −0.04 to −0.05 bar was applied during extrusion. The resultingextrudate was water cooled and cut into pellets and was found to have amelt flow index of 8-10 g/10 min, at 190° C. with 2.16 kg.

The polymer composition prepared in accordance with Example 5 was formedinto a cast extruded sheet. The resulting sheet was tested according toASTM D-882 and found to exhibit a tensile strength at break of >15 MPa,an elongation at break of >400%, and a dart drop impact strength (inaccordance with GB1843) of >20 kJ/m². The sheet was also found to fullycomply with the biodegradability requirements of EN 13432.

EXAMPLE 6: PREPARATION OF A BIODEGRADABLE POLYMER COMPOSITION

A composition consisting of 40 wt. % MB-1, 10 wt. % PCL and 50 wt. % PLAwas first dry blended and then melt mixed using a ZSK-58 Twin ScrewExtruder with a rotational speed of 200 rpm. The temperature profile ofthe extruder was set at 90° C./160° C./185° C./185° C/175° C./165° C. Avacuum of −0.04 to −0.05 bar was applied during extrusion. The resultingextrudate was water cooled and cut into pellets and was found to have amelt flow index of 15-20 g/10 min, at 190° C. with 2.16 kg.

The polymer composition prepared in accordance with Example 6 was formedinto a rigid sheet material. The resulting sheet was tested according toASTM D-882 and found to exhibit a tensile strength at break (machinedirection) of ≧20 MPa, a tensile strength at break (transversedirection) ≧15 MPa, an elongation at break (machine direction) of ≧250%,and an elongation at break (transverse direction) of ≧150%. The sheetwas also found to fully comply with the biodegradability requirements ofEN 13432.

EXAMPLE 7: PREPARATION OF A BIODEGRADABLE POLYMER COMPOSITION

A composition consisting of 65 wt. % biodegradable aromatic/aliphaticcopolyester PBAT (e.g. Enpol G8060), 10% MB-1, 20 wt. % calciumcarbonate (2 micron particle size, micronized oyster shells) and 5 wt. %titanate coupling agent, was first dry blended and then melt mixed usinga ZSK-65 Twin Screw Extruder with a rotational speed of 220 rpm. Thetemperature profile of the extruder was set at 80° C./130° C./165°C./165° C./155° C./130° C. A vacuum of 0.04 to 0.05 bar was appliedduring extrusion. The resulting extrudate was water cooled and cut intopellets and was found to have a melt flow index of 12 g/10 min, at 190°C. with 2.16 kg.

The polymer composition prepared in accordance with Example 7 was blowninto film having a thickness of approximately 20 micron. The resultingfilm was tested according to ASTM D-882 and found to exhibit a tensilestrength at break of >15 MPa and an elongation at break of >600%. Thefilm was also found to fully comply with the biodegradabilityrequirements of EN 13432.

EXAMPLE 8: PREPARATION OF MASTERBATCH FROM STARCH AND PBAT (MB-2)

35 kg of acidic ester starch (DS of 0.5) having a water content of<1 wt.%, 20 kg of glycerol, 20 kg of ethyleneacrylic acid (9% acid, melt flowindex=20), 12 kg PBAT, 1 kg of distilled monoglyceride, 0.16 kg sodiumhydroxide dissolved in a minimum amount of water, 0.3 kg calciumstearate, and 0.2 kg stearic acid were melt mixed in a ZSK-65 Twin ScrewExtruder (L/D=48). Prior to melt mixing these components, the solidmaterials were dry blended in a high speed mixer and then the liquidmaterials then added to provide for a uniform distribution of allcomponents. The polymer melt was extruded as a strand, air cooled andcut into pellets.

EXAMPLE 9: PREPARATION OF BIODEGRADABLE POLYMER COMPOSITION

A composition consisting of 50 wt. % MB-2, 30 wt. % PCL and 20 wt. %PBAT was first dry blended and then melt mixed using a ZSK-65 Twin ScrewExtruder with a rotational speed of 220 rpm. The temperature profile ofthe extruder was set at 80° C./130° C./165° C./165° C./155° C./130° C. Avacuum of −0.04 to −0.05 bar was applied during extrusion. The resultingextrudate was water cooled and cut into pellets and was found to have amelt flow index of 10 g/10 min at 190° C. with 2.16 kg.

The polymer composition prepared in accordance with Example 9 was blowninto film having a thickness of approximately 15 micron. The resultingfilm was tested according to ASTM D-882 and found to exhibit a tensilestrength at break of >14 MPa and an elongation at break of >400%. Thefilm was also found to fully comply with the biodegradabilityrequirements of EN 13432.

EN 13432 is a performance standard entitled “Packaging: Requirements forpackaging recoverable through composting and biodegradation; Test schemeand evaluation criteria for the final acceptance of packaging”.

EN 13432 is underpinned by the following test methods: ISO 16929 (12week disintegration test in compost), ISO 14855 (in vessel compostingtest for CO₂ evolution), heavy metals, compost quality, volatile solidsand the OECD 208 A germination test.

The European Norm EN 13432 and the American Society for Testing andMaterials (ASTM International) D6400-99 standards all definebiodegradability in respect of a time period of 6 months. In the case ofEN 13432 a material is deemed biodegradable if it will break down to theextent of at least 90% to H₂O and CO₂ and biomass within a period of 6months. While for the ASTM D-6400 it is necessary for the material tobreak down to the extent of at least 60%.

Both standards state that in order for a product to be compostable thefollowing criteria need to be met:

1) Disintegration: the ability to fragment into non-distinguishablepieces after screening and safely support bio-assimilation and microbialgrowth;

2) Inherent Biodegradation: conversion of carbon to carbon dioxide tothe level of 60%, over a period of 180 days (as specified ASTM D6400-99)and 90% in 180 days for the European standard (EN 13432);

3) Safety: that there is no evidence of any eco-toxicity in finishedcompost and soils and it can support plant growth; and

4) Toxicity: that heavy metal concentrations are less than 50%recommended values.

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the word “comprise”, and variations such as“comprises” and “comprising”, will be understood to imply the inclusionof a stated integer or step or group of integers or steps but not theexclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (orinformation derived from it), or to any matter which is known, is not,and should not be taken as an acknowledgment or admission or any form ofsuggestion that that prior publication (or information derived from it)or known matter forms part of the common general knowledge in the fieldof endeavour to which this specification relates.

1. A masterbatch suitable for use in preparing a biodegradable polymercomposition, said masterbatch comprising the following components and/ortheir transesterification reaction product: (a) polysaccharide; (b)biodegradable polyester; (c) biodegradable polymer having pendantcarboxylic acid groups; and (d) transesterification catalyst.
 2. Themasterbatch according to claim 1, wherein the biodegradable polymerhaving pendant carboxylic acid groups is an ethylene acrylic acidcopolymer.
 3. A method of preparing a masterbatch suitable for use inthe manufacture of a biodegradable polymer composition, said methodcomprising melt mixing in the presence of a transesterification catalysta polysaccharide, a biodegradable polyester and a biodegradable polymerhaving pendant carboxylic acid groups.
 4. The method of preparing amasterbatch according to claim 3, wherein the biodegradable polymerhaving pendant carboxylic acid groups is an ethylene acrylic acidcopolymer.